1. Field of the Invention
The present invention relates to an apparatus and method for bar coating, and more particularly, to an apparatus and method for bar coating which applies a coating liquid to a continuously running web with a columnar bar having a small diameter of 5 mm to 15 mm inclusive.
2. Description of the Related Art
Conventionally, various methods are proposed as methods of applying a coating liquid to a continuously running web, and as shown in Japanese Patent Application Laid-Open No. S58-4589 or the like, a bar coating method which is easy to operate and does not require much space is widely used. However, since the bar is long, stepped coating thickness unevenness (hereinafter, referred to as “traverse step-like unevenness”) are likely to occur in the web running direction due to minute vibration of the web or the bar, and as a countermeasure for this, the applicant of the present invention proposed, in Japanese Patent Application Laid-Open No. H09-201563, a bar coating method whereby, when it is assumed that a lap angle between the web and the bar is 2.5° to 30° inclusive, the maximum diameter of the bar cross-section is Rb and the curvature radius of the arc of the cross-section of the bar receiving member of the bar support member is Rh, Rb/Rh is set to within a range from 0.9 to 1.0 inclusive and the bar hold angle of the bar support member is set to 90° to 180° inclusive. In this way, it is possible to solve traverse step-like unevenness.
Furthermore, Japanese Patent Application Laid-Open No. 2006-82059 proposes to adjust straightness and roundness of the whole bar in order to apply a thin film to the web without producing traverse step-like unevenness.
However, even when the bar coating methods according to Japanese Patent Application Laid-Open No. H09-201563 and Japanese Patent Application Laid-Open No. 2006-82059 are used, there is a problem that traverse step-like unevenness occurs in the web width direction for every turn of the bar on the coating surface of the web onto which the coating liquid has been applied. Especially, as for thin film coating applied to a web where a wet film thickness is 15 μm or less as in the case of coating when manufacturing an optically functional film such as optically compensated film, it is difficult to obtain a leveling effect after coating and these coating faults become easily apparent, which is problematic.
However, even if the straightness or roundness of the whole bar is adjusted, there is a problem that the occurrence of traverse step-like unevenness cannot be prevented during bar coating.
The present invention has been implemented in view of the above described circumstances and it is an object of the present invention to provide an apparatus and method for bar coating capable of applying a coating liquid to a web as a thin film so as not to produce any traverse step-like unevenness during bar coating.